How Viagra Works

Erections work kind of like a balloon filled with pressurized blood instead of pressurized air.

HowStuffWorks.com

When you want to move nearly any part of your body, you do it using muscles. Whether you're moving your fingers, toes, arms or legs, muscles do the work. Even when you stick your tongue out, you do it using muscles:

You think about moving some part of your body.

The appropriate muscles contract.

That part of the body moves.

Muscles let you move your body voluntarily with precise control.

The penis, on the other hand, is completely different. There are no muscle contractions involved in making the penis erect. To become erect, the penis instead uses pressure.

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The penis handles two tasks: urination and ejaculation.

HowStuffWorks.com

Probably the easiest way to understand how the penis becomes erect is to think about a balloon. If a balloon has no air in it, it's limp. As you inflate a limp balloon with just a little air, it becomes elongated and rigid.

The penis uses a similar mechanism, but instead of using pressurized air to become rigid, the penis uses pressurized blood. The penis contains two cigar-shaped structures, called corpora cavernosa (singular: corpus cavernosum), that it uses to become erect.

Think of the corpora cavernosa as balloonlike tubes. Arteries­ bring blood into these two tubes, and veins carry blood away from them. The penis can be either limp or erect, depending on the flow of blood:

In a non-erect state, the arteries that transport b­lood into the corpora cavernosa are somewhat constricted, while the veins that drain the blood from the penis are open. There is no way for pressure to build inside the penis. In this state, the penis is limp.

When a man becomes aroused, the arteries leading into the penis open up so that pressurized blood can enter the penis quickly. The veins leaving the penis constrict. Pressurized blood is trapped in the corpora cavernosa, and this blood causes the penis to elongate and stiffen. The penis is erect.

If the arteries leading to the penis don't open up properly, it's difficult or impossible for a man's penis to become erect. This problem is the leading cause of erectile dysfunction (ED).

To solve an erection problem when the cause is poor blood flow, you need to open the arteries. Let's take a look at how this can be done -- and how it was done before Viagra.